1. Field of the Invention
The present invention relates to an organic electroluminescent display device, and more particularly, to a method of fabricating an organic electroluminescent display device.
2. Discussion of the Related Art
The demand for thinner flat panel display devices has increased with the demand for large-sized display devices. One type of thin flat panel display, the electroluminescent display device (ELD) has received increased attention.
ELD devices may be classified either as inorganic electroluminescent display devices and organic electroluminescent display devices depending upon the type of material used in their construction. Organic ELD device have the advantage they can be driven with a lower voltage (e.g., less than 10V) than plasma display panels or inorganic ELD devices. In an organic ELD device, pairs of electrons are created by injecting electrical charges are injected into an organic emitting layer provided between a hole injection electrode (cathode) and an electron injection electrode (anode). Recombination of the created electrons and holes results in the emission of light. Because of their advantages, organic ELD devices are being actively researched and developed.
FIG. 1 schematically illustrates the structure of a typical organic electroluminescent display device. As illustrated in FIG. 1, a typical organic electroluminescent display device 10 has a cathode electrode 3 and an anode electrode 1 facing into each other on a transparent substrate, such as a glass substrate. By applying a voltage between the cathode electrode 3 and the anode electrode 1, light is emitted from an organic emitting layer 5 formed between the anode electrode 1 and the cathode electrode 3. The anode electrode 1 may be formed of a transparent conductive material such as indium-tin-oxide (ITO) that readily supplies holes and facilitates the emission of light from the device. The cathode electrode 3 may be formed of a metal haying a low work function to allow electrons to be easily supplied.
Accordingly, if a positive (+) voltage and a negative (−) voltage are respectively applied to the anode electrode 1 and the cathode electrode 3, the holes injected from the anode electrode 1 and the electrons injected from the cathode electrode 3 are re-combined in the organic emitting layer, thereby causing the emission of light. The color of the emitted light depends on the material forming the organic emitting layer 5. For example, R (red), G (green), and B (blue) emission colors may be variously emitted by organic emitting layers 5 including appropriately selected materials.
An organic luminescent device may include a plurality of unit pixels arranged in a matrix. By selectively driving the organic emitting layer of the unit pixels using a driving device and a switching device provided at each unit pixel, an image may be displayed. The driving device and the switching device may each include a thin film transistor.
In an organic luminescent device of the related art, three R, G, and B unit pixels constitute a basic unit for driving. The organic emitting layer of the organic electroluminescent display device can be formed by various methods of the related art including a shadow mask method, an inkjet method, a laser induced transfer imaging (LITI) method, and a micropattterning method.
The shadow mask method is a method of forming RGB emitting layers on a substrate for film formation by alignment by using a mask having open portions corresponding to the organic emitting layer regions. However, this method is not easily usable for the manufacture of large-area display devices because problems such as alignment errors make obtaining a high resolution using mask processing difficult.
The inkjet method is a method that is mainly used for polymers, in which a liquid phase polymer is dripped onto a desired position by an inkjet to form the respective RGB emitting layers.
The LITI method is a method in which respective RGB emitting layers are formed on a polymer film having a heat absorption layer, placed and aligned on a substrate, and then sequentially transferred by applying heat specifically to a desired pattern position using a laser. The LITI method requires an additional polymer film for transfer, and is difficult to perform.
The micropatterning method is a method in which an epoxy mold is placed on a substrate on which an emitting layer is formed, and pressed with a predetermined pressure to remove undesired portions from the emitting layer. The micropatterning method is unsuitable for manufacturing an organic electroluminescent display device because peripheral portions of the pattern are not kept clean. Moreover, the epoxy mold becomes larger as the area of a display device becomes larger, making it difficult to apply a uniform pressure throughout the entire substrate. Accordingly, the micropatterning method of the related art is not suitable for reliable manufacture of large-area display devices.